High power semiconductor lasers are used to pump cladding pumped fiber lasers. Fiber lasers are capable of producing output power in the multiple kW range and are used in a variety of applications that require high output power such as cutting, welding, material processing (e.g., marking, engraving, and cutting) and directed energy. Achieving the power levels required for these applications is often accomplished by combining the fiber-coupled outputs of multiple lower power diode modules to pump active fibers.
When combining diode pumped fibers it is often convenient to perform the beam combination of the coupled fibers with a fiber based beam combiner that couples a plurality of optical fibers to a single output fiber. Conventionally, combining multiple fibers to achieve higher power can either reduce beam efficiency or beam quality. High power (kilowatt-class) fiber pump, pump-signal and signal combiners are vulnerable to small imperfections and losses which have significant impact on reliability.
In general, a process of fabricating a high power combiner includes significant physical manipulation of the optical fibers in the bundle. For example, often optical output fibers of the bundle are fused, twisted and tapered into an hourglass shape, and cleaved at the waist. Conventionally, tapering of the bundle of fibers requires the cross-sectional area of the untapered fiber bundle to be narrowed down to a cross-sectional area of the single output fiber. Once the fiber bundle is cleaved, the output end of the tapered fiber bundle is spliced (or otherwise coupled) onto an output fiber. All of this physical manipulation may result in structural defects such as micro-bends in the fibers or cladding which can introduce loss and/or degradation in beam quality or efficiency. Further, due to the twisting of optical fibers needed to achieve high coupling efficiency they are difficult to handle. What is needed is a method of reducing the amount of physical manipulation of the optical fibers associated with the fabrication of optical fiber combiners.